A Long Island store employee handed over a lost $19,000 diamond ring to the wrong woman after the customer falsely claimed it was hers, cops said yesterday.

The ring had slipped off the 42-year-old owner’s finger as she was reaching into her purse at a Target store in Commack on May 6. She then left the store without realizing it was gone.

An employee soon spotted the jewel-encrusted ring and ran out to the parking lot to return it.

Unfortunately, he found a different woman with a similar hair style and black raincoat, and asked her if she had lost a ring made up of 12, half-carat princess-cuts placed around a platinum eternity band.

According to police sources, the woman at first said, “Oh, maybe.”

Then the worker showed her the pricey jewelry and she said, “S–t, that’s my ring!”

“Thank you very much, have a nice day,” the sneaky bauble bandit said. She hasn’t been seen since.

The victim — a mom of three who asked that only her first name, Maryann, be used — soon returned to the store after realizing the ring was gone and was stunned to find out it had been handed to another woman.

“She wasn’t looking to go steal something, but they put it in her hand and I guess she thought it was hers,” Maryann said. “She could be wearing it right now.”

She also was upset at the worker, who handed the ring over without trying to get the woman to describe it, or otherwise prove she owned it.

Maryann said it had been a 10th-anniversary gift from her contractor-husband.

Police have been trying to track down the ring thief, but the woman paid cash for her purchases, leaving no paper trail.

Yesterday, they released a blurry security photo of the woman, and asked anyone with information to call (800) 220-TIPS. There is a $5,000 re ward.

“The ring meant a lot to me,” she said. “My husband worked hard to buy me that ring. No mat ter what the circumstances, it’s not hers. The insurance company paid me, but I don’t want the money, I want the ring back.”